The invention relates generally to an internal combustion engine, especially a direct-injection, compression-ignition or spark-ignition internal combustion engine.
More particularly, the invention relates to a fuel injection method and arrangement for an internal combustion engine.
A known direct-injection, compression-ignition or spark-ignition internal combustion engine is provided with a combustion chamber having the shape of a body of rotation. An air swirl is generated in the combustion chamber and fuel is injected into the latter via an injection nozzle.
It is recognized that there are advantages to be obtained by matching the fuel injection conditions to the operating condition of the engine. For instance, it has been found that a compact fuel jet is advantageous during operation at full load and high speed. Such a jet causes the greatest possible amount of fuel to be deposited on, or at least transported to the vicinity of, the hot wall of the combustion chamber. The fuel deposited on or brought into the vicinity of the combustion chamber wall evaporates. Mixing of the fuel with the air is effected mainly by the air swirl generated in the combustion chamber.
Many of the conventional internal combustion engines are equipped with injection nozzles which are provided with an opening of constant cross-sectional area. In order to obtain a compact fuel jet with an injection nozzle of this type, the cross-sectional area of the opening must be large. Fuel injection takes place at a relatively low pressure.
During operation at no load or in the low load range at low speed, it is of advantage for the fuel to be injected in the form of a finely atomized spray so that the fuel mixes with the air directly and does not reach the combustion chamber wall which, in this case, is relatively cold. Mixing of the fuel and the air as well as combustion take place rapidly and completely and there are no uncombusted fuel fractions to be exhausted. This mode of fuel injection is also applicable for cold starting and for running up a cold engine. Mixture formation is here mainly a function of fuel atomization which, in turn, depends primarily upon the relative velocity of the fuel and air.
In order to obtain a finely atomized fuel spray from a nozzle having an opening of constant cross-sectional area, the opening must be small. For a given fuel delivery rate, this results in a relatively high fuel velocity and relatively high pressure at the opening.
In an attempt to obtain satisfactory fuel injection characteristics under all operating conditions, it was proposed to use an injection nozzle having an opening of variable cross-sectional area, e.g. a throttling pintle nozzle. Although some improvement was achieved relative to an injection nozzle having an opening of constant cross-sectional area, the benefits were realized under only some operating conditions of the engine. Generally, improvement was obtained only in the uppermost and lowermost load ranges. Furthermore, the benefits were inconsistent and could not be adequately controlled.